At least 95 people have been killed amid fighting that erupted this week among rival rebel groups near the Syrian capital, Damascus, a monitoring group reported on Sunday.
The fatalities included 87 rebel fighters and eight civilians, the Syrian Observatory for Human Rights added.
The violence first broke out on Friday in the key opposition stronghold of Eastern Ghouta, on the eastern edge of Damascus.
The fighting pits Jaish al-Islam, a main rebel group in the area, against Faylaq al-Rahman and its al-Qaida-linked ally Jabhat Fatah al-Sham, the watchdog added.
They were engaged in fierce clashes on Sunday after each side has reinforced its forces, the Observatory said.
In recent weeks, each group has accused the other of attacking its followers in the government-besieged area.
Last year, hundreds of insurgents and civilians were killed in fighting among rebel factions in Eastern Ghouta.
In recent months, Syrian forces, backed by Russia, have made territorial gains against the armed forces in different parts of the war-wracked country.
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